1. Technical Field
The present invention relates to an atomic resonance transition device, an atomic oscillator, a timepiece, an electronic apparatus and a moving object.
2. Related Art
As an oscillator with highly accurate oscillation characteristics stable for a long term, an atomic oscillator is known which oscillates based on an energy transition of atoms of alkali metal such as rubidium or cesium.
In general, the operation principle of the atomic oscillator is roughly classified into a system using a double resonance phenomenon caused by light and microwaves and a system using coherent population trapping (CPT) caused by two types of lights having different wavelengths. Since the atomic oscillator using the coherent population trapping can be miniaturized as compared with the atomic oscillator using the double resonance phenomenon, in recent years, the former atomic oscillator is expected to be mounted on various equipments (see, for example, JP-A-2011-160251 (Patent Literature 1)).
As disclosed in, for example, Patent Literature 1, the atomic oscillator using the coherent population trapping includes a gas cell in which a gaseous alkali metal atom is sealed, a light source to emit a resonant light pair (first and second light) for resonating the alkali metal atom in the gas cell, and a light detection part to detect the resonant light pair passing through the gas cell. In the atomic oscillator as stated above, an EIT (Electromagnetically Induced Transparency) phenomenon occurs in which when a frequency difference between two types of resonant lights is a specific value, both the two types of resonant lights are not absorbed by the alkali metal atom in the gas cell and pass through. The light detector detects an EIT signal as a sharp signal generated by the EIT phenomenon, and the EIT signal is used as a reference signal.
Besides, in the atomic oscillator of Patent Literature 1, in order to achieve miniaturization of a circuit portion and power saving, frequency control is performed based on a beat signal obtained by interference between plural lights passing through the gas cell, so that the first and second light become the resonant light pair to cause the EIT phenomenon.
However, in the atomic oscillator using the coherent population trapping, that is, in the atomic oscillator using the EIT signal as the reference signal, a constant magnetic field is generally applied to the alkali metal atom in the gas cell. Thus, also in the atomic oscillator disclosed in Patent Literature 1, a coil for generation the magnetic field, a shield for shielding an external magnetic field and the like are required, and consequently, there is a problem that miniaturization of the device can not be sufficient achieved.